German Published Patent Application No. 196 26 576 an electromagnetically operable fuel injector describes in which, for the electromagnetic actuation, an armature cooperates with an electrically energizable magnetic coil, and the lift of the armature is transmitted to a valve-closure member via a valve needle. The valve-closure member interacts with a valve-seat surface to form a sealing seat. Several fuel channels are provided in the armature. The armature is reset by a resetting spring.
An electromagnetically operable fuel injector is also described in German Published Patent Application No. 195 03 821, in which an armature also cooperates with an electrically energizable magnetic coil. The lift of the armature is transmitted to a valve-closure member by a valve needle.
What is disadvantageous about the fuel injectors known from the above-named documents is particularly the lack of free flow space for the fuel, which is caused by the positioning of the valve needle in a hollow recess in the armature. This leads to big pressure differences between the upper and the lower sides of the armature, particularly during movement of the armature, since pressure equalization is hindered. The diameter of borings in the armature, put there to make it possible for the fuel to pass through, is limited because of the necessary armature pole surface and the low space availability.
It is also disadvantageous that the hydraulic pressure force of the fuel on the armature leads especially to longer valve opening times, which has a corresponding effect on the quantity of fuel metered in. On the other hand, due to fluctuations in the pressure difference, for example, in the case of different temperatures of the fuel injector, and viscosity differences resulting from this, variations in the switching time of the fuel injector are caused, which, in addition to the increased length of the switching times, lead to metering in irregular quantities of fuel.